Precessional spin current structure for MRAM

ABSTRACT

A magnetoresistive random-access memory (MRAM) is disclosed. MRAM device has a magnetic tunnel junction stack having a significantly improved performance of the free layer in the magnetic tunnel junction structure. The MRAM device utilizes a precessional spin current (PSC) magnetic layer in conjunction with a perpendicular MTJ where the in-plane magnetization direction of the PSC magnetic layer is free to rotate. The precessional spin current magnetic layer is constructed with a material having a face centered cubic crystal structure, such as permalloy.

FIELD

The present patent document relates generally to spin-transfer torquemagnetic random access memory and, more particularly, to a magnetictunnel junction stack having improved performance of the free layer inthe magnetic tunnel junction structure through use of a precessionalspin current structure having high in-plan anisotropy through the use ofmaterials having face centered cubic materials.

BACKGROUND

Magnetoresistive random-access memory (“MRAM”) is a non-volatile memorytechnology that stores data through magnetic storage elements. Theseelements are two ferromagnetic plates or electrodes that can holdmagnetization and are separated by a non-magnetic material, such as anon-magnetic metal or insulator. In general, one of the plates has itsmagnetization pinned (i.e., a “reference layer”), meaning that thislayer has a higher coercivity than the other layer and requires a largermagnetic field or spin-polarized current to change the orientation ofits magnetization. The second plate is typically referred to as the freelayer and its magnetization direction can be changed by a smallermagnetic field or spin-polarized current relative to the referencelayer.

MRAM devices store information by changing the orientation of themagnetization of the free layer. In particular, based on whether thefree layer is in a parallel or anti-parallel alignment relative to thereference layer, either a “1” or a “0” can be stored in each MRAM cell.Due to the spin-polarized electron tunneling effect, the electricalresistance of the cell change due to the orientation of themagnetization of the two layers. The cell's resistance will be differentfor the parallel and anti-parallel states and thus the cell's resistancecan be used to distinguish between a “1” and a “0”. One importantfeature of MRAM devices is that they are non-volatile memory devices,since they maintain the information even when the power is off. The twoplates can be sub-micron in lateral size and the magnetization directioncan still be stable with respect to thermal fluctuations.

Spin transfer torque or spin transfer switching, uses spin-aligned(“polarized”) electrons to change the magnetization orientation of thefree layer in the magnetic tunnel junction. In general, electronspossess a spin, a quantized number of angular momentum intrinsic to theelectron. An electrical current is generally unpolarized, i.e., itconsists of 50% spin up and 50% spin down electrons. Passing a currentthough a magnetic layer polarizes electrons with the spin orientationcorresponding to the magnetization direction of the magnetic layer(i.e., polarizer), thus produces a spin-polarized current. If aspin-polarized current is passed to the magnetic region of a free layerin the magnetic tunnel junction device, the electrons will transfer aportion of their spin-angular momentum to the magnetization layer toproduce a torque on the magnetization of the free layer. Thus, this spintransfer torque can switch the magnetization of the free layer, which,in effect, writes either a “1” or a “0” based on whether the free layeris in the parallel or anti-parallel states relative to the referencelayer.

FIG. 1 illustrates a magnetic tunnel junction (“MTJ”) stack 100 for aconventional MRAM device. As shown, stack 100 includes one or more seedlayers 110 provided at the bottom of stack 100 to initiate a desiredcrystalline growth in the above-deposited layers. Furthermore, MTJ 130is deposited on top of SAF layer 120. MTJ 130 includes reference layer132, which is a magnetic layer, a non-magnetic tunneling barrier layer(i.e., the insulator) 134, and the free layer 136, which is also amagnetic layer. It should be understood that reference layer 132 isactually part of SAF layer 120, but forms one of the ferromagneticplates of MTJ 130 when the non-magnetic tunneling barrier layer 134 andfree layer 136 are formed on reference layer 132. As shown in FIG. 1,magnetic reference layer 132 has a magnetization direction perpendicularto its plane. As also seen in FIG. 1, free layer 136 also has amagnetization direction perpendicular to its plane, but its directioncan vary by 180 degrees.

The first magnetic layer 114 in the SAF layer 120 is disposed over seedlayer 110. SAF layer 120 also has a antiferromagnetic coupling layer 116disposed over the first magnetic layer 114. Furthermore, a nonmagneticspacer 140 is disposed on top of MTJ 130 and a polarizer 150 is disposedon top of the nonmagnetic spacer 140. Polarizer 150 is a magnetic layerthat has a magnetic direction in its plane, but is perpendicular to themagnetic direction of the reference layer 132 and free layer 136.Polarizer 150 is provided to polarize a current of electrons(“spin-aligned electrons”) applied to MTJ structure 100. Further, one ormore capping layers 160 can be provided on top of polarizer 150 toprotect the layers below on MTJ stack 100. Finally, a hard mask 170 isdeposited over capping layers 160 and is provided to pattern theunderlying layers of the MTJ structure 100, using a reactive ion etch(RIE) process.

Various mechanisms have been proposed to assist the free-layermagnetization switching in magnetic tunnel junction (MTJ) devices suchas orthogonal spin transfer for in plane magnetic tunnel junctiondevices. One issue has been that to realize the orthogonal spin transfereffect for in-plane MTJ structures, large spin currents may be requiredfor switching. The need for large switching currents may limit suchdevice's commercial applicability. One way proposed to reduce switchingcurrent is to lower the magnetization of the free layer. However, if theeffective magnetization of the free layer is lowered significantly, theorthogonal effect has to be limited so that the free-layer does not gointo precessional mode that would make the end state of the free-layermagnetization un-deterministic. This defines the operation window forthe in-plane OST structures. In an in-plane device, unlike that shown inFIG. 1, the magnetization direction of the reference layer and freelayer are in the plane of the layer. Another aspect of in-plane devicesis that the thermal stability requirements may limit the size of the MTJdevices to approximately sixty nanometers or higher.

For perpendicular MTJ structures such as those shown in FIG. 1, theprecession is not an issue. The orthogonal polarizer acts on the freelayer magnetization at the initial state, but when the precession takeshold, the fixed orthogonal polarizer 150 helps only half the cycle ofthe free-layer magnetization rotation while it harms the other half ofthe cycle. This is demonstrated with reference to FIGS. 2A-2B and 3.FIGS. 2A-2B show switching of a free layer 136 of an MTJ. As is seen,free layer 136 has a magnetization direction 200 perpendicular to thatof the polarizer 150. The magnetization direction 200 of the free layer136 can rotate by 180 degrees. FIGS. 2A-2B show precession about theaxis of the magnetization vector of free layer 136. During precession,magnetic vector 200 begins to rotate about its axis in a cone-likemanner such that its magnetization vector 200′ deflects from theperpendicular axis 202 of free layer 136. For an ideal case, prior toinitiating precession, no component of magnetic vector 200 is in theplane of free layer 136, once precession starts, a component of magneticvector 200′ can be found both in-plane and orthogonal to free layer 136.As magnetic vector 200′ continues to precess (i.e., switch), therotation of vector 200′ extends further from the center of free layer136, as is seen in FIG. 2B.

In prior MTJ devices using a polarizer such as polarizer 150, themagnetization direction of polarizer 150 is fixed, which is shown inFIGS. 1 and 3. See also U.S. Pat. No. 6,532,164, which states that thedirection of the magnetization of the polarizing layer cannot vary inthe presence of current. Prior to current passing through the MTJ, thefree layer 136 has a magnetization direction 200 substantiallyperpendicular to that of the polarizer 150. While the magnetizationdirection 200 of the free layer 136 can rotate by 180 degrees, suchrotation is normally precluded by the free layer's inherent dampingability 205, which is represented by a vector 205 pointing to axis 202(shown as a dashed line in FIG. 2A as well as FIG. 3). Axis 202 isperpendicular to the plane of free layer 136. This damping 205 hasvalue, defined by the damping constant, which maintains themagnetization direction of the free layer 136.

Passing a current through polarizer 150 produces a spin-polarizedcurrent, which creates a spin transfer torque 210 in the direction ofthe polarizer 150 on the magnetization vector 200. This spin transfertorque from the polarizer adds to the main spin transfer torque thatcauses free layer magnetization direction switching. In devices likethose shown in FIG. 1, when the spin transfer torque 210 begins to helpovercome the damping 205 inherent to the free layer 136, the magneticdirection 200′ begins to precess about its axis, as shown in FIG. 2A. Asseen in FIG. 3, spin transfer torque 210 helps the magnetizationdirection of the free layer 136 to precess in a cone-like manner aroundan axis 202 perpendicular to the plane of the layers. When a spinpolarized current traverses the stack 100, the magnetization of the freelayer 136 precesses in a continuous manner (i.e. it turns on itself in acontinuous manner as shown in FIG. 3) with maintained oscillations untilthe magnetic direction of free layer 136 is opposite the magneticdirection prior to the spin torque causing precession, i.e., themagnetic direction of free layer 136 switches by 180 degrees.

FIG. 3 illustrates precession of a free layer 136 of an MTJ assisted byspin polarized current provided by polarizing magnetic layer 150. Thespin polarized electrons from polarizer 150 provide torque 210 thathelps overcome the damping 205 in the first half of the precession 215because the torque 210 provided by the spin polarized current isopposite that of the inherent damping 205 of the free layer 136. This isshown on the right-hand side of the middle portion of FIG. 3. However,the spin polarized electrons from polarizer 150 actually harm theswitching process during the second half of the precession 220. Thereason for this is that the spin of the electrons in the spin polarizedcurrent only apply a torque 210 in the direction of their polarization.Thus, when the magnetic vector is in the half of the precession cycle220 that is opposite the spin of the polarized electrons, the spintransfer torque 210 actually works with the inherent damping 205 of freelayer 136 to make rotation more difficult. This is shown in theleft-hand side of the middle portion of FIG. 3. Indeed, it is themagnetization vector of the reference layer 132 (not shown in FIG. 3)that overcomes the damping of free layer 136 as well as the spintransfer torque 210 during the half of a precession cycle where the spinof the electrons harms precession, and thus it is the reference layer132 that allows for completion of precession.

In these prior devices, because magnetization direction of polarizer 150is fixed, once the precession holds, it has no positive effect on theswitching mechanism for a full one-hundred eighty degree precession.This is because polarized electrons will help the spin transfer torquethe most when all vectors are closely aligned.

In U.S. patent application Ser. No. 14/814,036, filed by the sameApplicant as the present patent document, discloses an MRAM devicehaving a precessional spin current magnetic layer that is physicallyseparated from the free magnetic layer of a magnetic tunnel junction andwhich is coupled to the free magnetic layer by a non-magnetic spacer. Inthe device described in this co-pending application, the magnetizationdirection of the precessional spin current magnetic layer followsprecession of the magnetization direction of the free magnetic layer,thereby causing spin transfer torque to assist switching of themagnetization vector of the free magnetic layer. The disclosure of U.S.patent application Ser. No. 14/814,036 is incorporated by reference inits entirety.

When using an in-plane precessional spin current magnetic layer with aperpendicular magnetic tunnel junction, it is desirable to maintain themagnetic moment of the precessional spin current magnetic layer in-planewhile also reducing its magnetic moment. Unfortunately, manyferromagnetic materials such as CoFeB have interface perpendicularmagneto crystalline anisotropy (“IPMA”), thus resulting in a magneticdirection that is out of plane. To avoid IPMA, the thickness of theCoFeB must be increased, generally to thickness greater than 1.5 nm.However, a 1.5 nm thick layer of CoFeB layer increases the magneticmoment such that it is equal to or greater than the magnetic moment ofthe free layer, hence losing the ability to set the in-planemagnetization for low magnetic moment of the precessional spin currentmagnetic layer independently. This is undesirable because theprecessional spin current magnetic layer should remain in plane, and, asdiscussed, performance may be enhanced with the magnetic moment of theprecessional spin current magnetic layer is reduced. This results instrong dipolar fields in the vicinity of the free layer of the magnetictunnel junction, which decreases free layer stability.

SUMMARY

An MRAM device is disclosed that has a magnetic tunnel junction stackhaving a significantly improved performance of the free layer in themagnetic tunnel junction structure that requires significantly lowerswitching currents and which significantly reduces switching times forMRAM applications.

In an embodiment, a magnetic device includes a first syntheticantiferromagnetic structure in a first plane. The syntheticantiferromagnetic structure includes a magnetic reference layer, wherethe magnetic reference layer has a magnetization vector that isperpendicular to the first plane and has a fixed magnetizationdirection. An embodiment also includes a non-magnetic tunnel barrierlayer in a second plane and disposed over the magnetic reference layer.An embodiment further includes a free magnetic layer in a third planeand disposed over the non-magnetic tunnel barrier layer. The freemagnetic layer has a magnetization vector that is perpendicular to thethird plane and has a magnetization direction that can precess from afirst magnetization direction to a second magnetization direction. Themagnetic reference layer, the non-magnetic tunnel barrier layer and thefree magnetic layer form a magnetic tunnel junction. The embodimentfurther includes a non-magnetic spacer in a fourth plane that isdisposed over the free magnetic layer. The magnetic coupling layercomprises MgO. In an embodiment, a precessional spin current magneticlayer is present in a fifth plane that is physically separated from thefree magnetic layer and coupled to the free magnetic layer by thenon-magnetic spacer. The precessional spin current magnetic layer has amagnetization vector with a magnetization component in the fifth planewhich can freely rotate in any magnetic direction. The precessional spincurrent magnetic layer comprising a material has a face centered cubic(fcc) crystal structure. An embodiment further includes a capping layerin a sixth plane that is disposed over the precessional spin currentmagnetic layer. Electrical current is directed through the cappinglayer, the precessional spin current magnetic layer, the non-magneticspacer, the free magnetic layer, the non-magnetic tunnel barrier layer,and the magnetic reference layer, wherein electrons of the electricalcurrent are aligned in the magnetic direction of the precessional spincurrent magnetic layer. The magnetization direction of the precessionalspin current magnetic layer is free to follow precession of themagnetization direction of the free magnetic layer, thereby causing spintransfer torque to assist switching of the magnetization vector of thefree magnetic layer.

In an embodiment of the magnetic device, the magnetization direction ofthe magnetization vector of the precessional spin current magnetic layeris in the fifth plane.

In an embodiment of the magnetic device, the magnetization direction ofthe precessional spin current magnetic layer has a magnetizationcomponent in the fifth plane which can freely rotate in the fifth plane.

In an embodiment of the magnetic device, the material having the facecentered cubic (fcc) crystal structure is permalloy comprising nickel(Ni) and iron (Fe).

In an embodiment of the magnetic device, the precessional spin currentmagnetic layer comprises an Fe layer, an Ru layer and a face centeredcubic crystal structure layer comprising the material having the facecentered cubic crystal structure. The Fe layer can be disposed over thenon-magnetic spacer, the Ru layer can be disposed over the Fe layer, andthe face centered cubic crystal structure layer can be disposed over theRu layer.

In an embodiment of the magnetic device, the material having the facecentered cubic crystal structure is permalloy comprising nickel (Ni) andiron (Fe).

In an embodiment of the magnetic device, the capping layer comprises alayer of TaN.

In an embodiment of the magnetic device, the precessional spin currentmagnetic layer comprises an Fe layer, an Ru layer, a CoFeB layer, and aface centered cubic crystal structure layer comprising the materialhaving the face centered cubic crystal structure. The Fe layer can bedisposed over the non-magnetic spacer, the Ru layer can be disposed overthe Fe layer, the CoFeB layer can be disposed over the Fe layer, and theface centered cubic crystal structure layer can be disposed over theCoFeB layer.

In an embodiment of the magnetic device, the material having the facecentered cubic crystal structure is permalloy comprising nickel (Ni) andiron (Fe).

In an embodiment of the magnetic device, the capping layer comprises alayer of TaN.

In an embodiment of the magnetic device, the precessional spin currentmagnetic layer comprises an Fe layer, an Ru layer, a first CoFeB layer,a face centered cubic crystal structure layer comprising the materialhaving the face centered cubic crystal structure and a second CoFeBlayer. The Fe layer can be disposed over the non-magnetic spacer, the Rulayer can be disposed over the Fe layer, the first CoFeB layer can bedisposed over the Fe layer, the face centered cubic crystal structurelayer can be disposed over the first CoFeB layer, and the second CoFeBlayer can be disposed over the face centered cubic crystal structurelayer.

In an embodiment of the magnetic device, the material having the facecentered cubic crystal structure is permalloy comprising nickel (Ni) andiron (Fe).

In an embodiment of the magnetic device, the capping layer comprises alayer of TaN.

In an embodiment of the magnetic device, the capping layer comprises alayer of MgO.

In an embodiment of the magnetic device, the capping layer comprises alayer Ru.

In an embodiment of the magnetic device, the precessional spin currentmagnetic layer comprises an Fe layer, and a NiFe layer, wherein the NiFelayer is the material having the face centered cubic crystal structure,the Fe layer being disposed over the non-magnetic spacer, the NiFe layerbeing disposed over the Fe layer. The precessional spin current magneticlayer further comprises a third layer being disposed over the NiFelayer.

In an embodiment of the magnetic device, the third layer comprisesCoFeB.

In an embodiment of the magnetic device, the precessional spin currentmagnetic layer is magnetically coupled to the free magnetic layer.

In an embodiment of the magnetic device, the precessional spin currentmagnetic layer is electronically coupled to the free magnetic layer.

In an embodiment of the magnetic device, precession of the precessionalspin current magnetic layer is synchronized to precession of the freemagnetic layer.

In an embodiment of the magnetic device, the precessional spin currentmagnetic layer has a rotation frequency greater than zero.

In an embodiment of the magnetic device, the free magnetic layer has aneffective magnetic anisotropy such that its easy magnetization axispoints away from the perpendicular direction and forms an angle withrespect to its perpendicular plane.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are included as part of the presentspecification, illustrate the presently preferred embodiments and,together with the general description given above and the detaileddescription given below, serve to explain and teach the principles ofthe MTJ devices described herein.

FIG. 1 illustrates a conventional MTJ stack for an MRAM device.

FIGS. 2A-2B illustrate the precession of the free layer in an MTJ.

FIG. 3 illustrates the precession of the free layer in an MTJ used witha polarizing magnetic layer having a fixed magnetization direction.

FIG. 4 illustrates the precession of the free layer in an MTJ used witha precessional spin current magnetic layer having a magnetizationdirection that rotates freely.

FIG. 5 illustrates an MTJ stack for an MRAM device having a precessionalspin current magnetic layer.

FIGS. 6A-6B are flow charts showing manufacturing steps for an MRAMdevice having a precessional spin current magnetic layer.

FIG. 7 illustrates an embodiment of an MTJ stack for an MRAM devicehaving a precessional spin current magnetic layer.

FIG. 8 illustrates an embodiment of an MTJ stack for an MRAM devicehaving a precessional spin current magnetic layer.

FIG. 9 illustrates an embodiment of an MTJ stack for an MRAM devicehaving a precessional spin current magnetic layer.

FIG. 10 illustrates the magnetic direction of the precessional spincurrent magnetic layer of an embodiment.

FIG. 11 is a graph of the thin film vibrating sample magnetometer (VSM)major hysteresis loop data for various perpendicular magnetic tunneljunction devices.

FIG. 12 is a graph illustrating ferromagnetic resonance (FMR) of an MRAMdevice having a precessional spin current magnetic layer.

FIG. 13 illustrates and alternative embodiment of an MTJ stack for anMRAM device having a precessional spin current magnetic layer.

The figures are not necessarily drawn to scale and the elements ofsimilar structures or functions are generally represented by likereference numerals for illustrative purposes throughout the figures. Thefigures are only intended to facilitate the description of the variousembodiments described herein; the figures do not describe every aspectof the teachings disclosed herein and do not limit the scope of theclaims.

DETAILED DESCRIPTION

The following description is presented to enable any person skilled inthe art to create and use a precessional spin current structure for amagnetic semiconductor device such as an MRAM device. Each of thefeatures and teachings disclosed herein can be utilized separately or inconjunction with other features to implement the disclosed system andmethod. Representative examples utilizing many of these additionalfeatures and teachings, both separately and in combination, aredescribed in further detail with reference to the attached drawings.This detailed description is merely intended to teach a person of skillin the art further details for practicing preferred aspects of thepresent teachings and is not intended to limit the scope of the claims.Therefore, combinations of features disclosed in the following detaileddescription may not be necessary to practice the teachings in thebroadest sense, and are instead taught merely to describe particularlyrepresentative examples of the present teachings.

In the following description, for purposes of explanation only, specificnomenclature is set forth to provide a thorough understanding of thepresent teachings. However, it will be apparent to one skilled in theart that these specific details are not required to practice the presentteachings.

This present patent document discloses a MRAM device that does not use apolarization layer having a fixed magnetization direction. Instead of apolarization layer having a fixed magnetization direction, the MRAMdevice described in this patent document utilizes a precessional spincurrent (PSC) magnetic layer 350 in conjunction with a perpendicular MTJ330 where the in-plane magnetization component direction of the PSClayer is free to rotate (and is shown, for example, in FIGS. 5 and 7).In one embodiment, the PSC magnetic layer 350 can rotate with thefree-layer magnetization precessional dynamics. This will significantlyimprove the impact of the spin current in overcoming the inherentdamping of the free layer 336 since the PSC layer will help the spintorque overcome this damping through the entire orbital motion of theprecession cycle rather on only half of the precession. Thisprecessional spin current effect throughout the entire one-hundredeighty degree rotation significantly enhances the free-layermagnetization switching.

FIG. 4 shows the concept behind the MRAM device using a PSC magneticlayer 350 having magnetization vector 270 that rotates instead of apolarization layer 150 having a magnetic vector with a fixedmagnetization direction. The free layer 336 in this embodiment issimilar to the free layer 136 previously discussed, in that it has aninherent damping characteristic 205 that can be overcome with theassistance of spin transfer torque. However, the embodiment shown inFIG. 4 replaces polarizing layer 150 with PSC magnetic layer 350. Asseen in the bottom portion of FIG. 4, the direction of the spin transfertorque 310 created by spin current passing through free layer 336changes with the rotation of the magnetization direction of the PSCmagnetic layer 350. As seen in the middle of FIG. 4, spin transfertorque 310 helps the magnetization direction 200′ of the free layer 336to precess in a cone-like manner around an axis 202 perpendicular to theplane of the layers. FIG. 4 shows a progression of rotation of themagnetic direction 200′ about axis 202. As discussed, when a spinpolarized current traverses the device, the magnetization of the freelayer 336 precesses in a continuous manner (i.e. it turns on itself in acontinuous manner as shown in FIG. 4) with maintained oscillations untilthe magnetic direction of free layer 336 is opposite the magneticdirection prior to the spin torque causing precession, i.e., themagnetic direction of free layer 136 switches by 180 degrees. Theprecessional spin current layer 350 and the free-layer 336 aremagnetically and/or electronically coupled such that the magnetizationdirection of the magnetization vector 270 of the PSC magnetic layer 350is free to follow the precessional rotation of the magnetic vector ofthe free layer 336. This can be seen in FIG. 4.

As seen in on the right-hand side of FIG. 4, the spin polarizedelectrons provide torque 310 helps to overcome the damping 205 in thefirst half of the precession 215 because the torque 310 provided by thespin polarized current is opposite that of the inherent damping 205 ofthe free layer 336. As discussed, the magnetization direction ofmagnetization vector 270 of PSC magnetic layer 350 rotates. Thus, thepolarization of electrons of the spin current created by PSC magneticlayer 350 changes as well. This means that the direction of torque 310exerted on magnetic vector of free layer 336 changes as well, which isseen on the bottom of FIG. 4. Thus, unlike prior devices having a fixedpolarization magnetic layer 150, the spin of the electrons in the spinpolarized current applies a torque 310 in both halves of the precessioncycle, including the half of the precession cycle 220 where devices withfixed polarization magnetic layers 150 actually harmed precession. Thisis seen in the left-hand side of FIG. 4. As is seen, the torque 310continues to help overcome the inherent damping 205 of free layer 136throughout the entire precession cycle. Thus, devices using PSC magneticstructure 350 can provide spin transfer torque 310 for an entireswitching cycle.

In an embodiment, the precessional vector 270 of the PSC magnetic layer350 is free to follow the precessional rotation of the magnetic vectorof the free layer 336. The magnetization direction of the free layer isswitched by the spin torque 310 from the reference layer 132 where thedirection of the current defines the final state.

A memory cell with a precessional spin current MTJ structure 300 isshown in FIG. 5. Memory cell 300 is formed on a substrate, which can besilicon or other appropriate materials, and can include complementarymetal oxide semiconductor (CMOS) circuitry fabricated thereon. MTJstructure 300 includes one or more seed layers 320 provided at thebottom of stack 300 to initiate a desired crystalline growth in theabove-deposited layers. A first synthetic antiferromagnetic (SAF) layer322 is disposed over seed layer 320. First SAF layer 322 is a magneticlayer having a magnetization direction that is perpendicular to itsplane. Details of the construction of first SAF layer 322 will bediscussed below. An anti-ferromagnetic (AFM) coupling layer 324 isdisposed over first SAF layer 322. AFM coupling layer 324 is anon-magnetic layer. A second SAF layer 326 is disposed over AFM couplinglayer 324. Second SAF layer 326 has a magnetic direction that isperpendicular to its plane. The magnetic direction of first SAF layer322 and second SAF layer 326 are antiparallel, as is shown in FIG. 5.Details of the construction of second SAF layer 326 will also bediscussed below. A ferromagnetic coupling layer 328 is placed oversecond SAF layer 326. Ferromagnetic coupling layer 328 is a non-magneticlayer. MTJ 330 is deposited over ferromagnetic coupling layer 328. MTJ330 includes reference layer 332, tunneling barrier layer (i.e., theinsulator) 334 and free layer 336. Reference layer 332 of MTJ 330 isfabricated over ferromagnetic coupling layer 328. Tunneling barrierlayer 334 of MTJ 330 is fabricated over reference layer 332. Free layer336 of MTJ 330 is fabricated over tunneling barrier layer 334. Note thatsynthetic antiferromagnetic layer 326 technically also includesferromagnetic coupling layer 328 and reference layer 332, but are shownseparately here for explanation purposes.

As shown in FIG. 5, the magnetization vector of reference layer 332 hasa magnetization direction that is perpendicular to its plane. As alsoseen in FIG. 5, free layer 336 also has a magnetization vector that isperpendicular to its plane, but its direction can vary by 180 degrees.In addition, free layer 336 design may include magnetization of the freelayer 336 pointing a few degrees away from its perpendicular axis. Thetilted angle of the free layer magnetization can be due to interactionwith the PSC magnetic layer 350 or due to magnetocrystalline anisotropy,will additionally help switching of the free layer magnetization byimproving the initiation of the switching. Because reference layer 332and free layer 336 each have a magnetic direction that is perpendicularto their respective planes, MTJ 330 is known as a perpendicular MTJ.

A nonmagnetic spacer 340 is disposed over of MTJ 330. PSC magnetic layer350 is disposed over nonmagnetic spacer 340. In one embodiment, PSCmagnetic layer 350 has a magnetization vector having a magneticdirection parallel to its plane, and is perpendicular to the magneticvector of the reference layer 332 and free layer 336. One or morecapping layers 370 can be provided on top of PSC layer 350 to protectthe layers below on MTJ stack 300.

Nonmagnetic spacer 340 has a number of properties. For example,nonmagnetic spacer 340 physically separates free layer 336 and PSC layer350. Nonmagnetic spacer 340 promotes strong magnetic and/or electroniccoupling such that the magnetic direction of the PSC magnetic layer 350is free to follow the precession cycle of the free layer 336. In otherwords, nonmagnetic spacer 340 couples the magnetic direction of the PSCmagnetic layer 350 to the magnetic direction of the free layer 336.Nonmagnetic spacer 340 transmits spin current efficiently from the PSCmagnetic layer 350 into the free layer 336 because it preferably has along spin diffusion length. Nonmagnetic spacer 340 also promotes goodmicrostructure and high tunneling magnetoresistance (TMR) and helps keepthe damping constant of the free layer 336 low.

PSC magnetic layer 350 has at least the following properties. First, inone embodiment, the magnetization direction of PSC magnetic layer 350 isin the plane of the layer but is perpendicular to magnetizationdirection of free layer 336. In other embodiments such as shown in FIG.10, the magnetization direction of PSC magnetic layer 350 can have ahorizontal component X and perpendicular component Z such that the angleΘ between the plane of free layer 336 and the magnetic direction 270 ofPSC magnetic layer 350 can be anywhere between 0 and less than 90degrees, although, as discussed, the angle is as close to zero asfeasible so that the magnetic direction remains in-plane. Likewise, asshown, the magnetization vector can also spin in a rotational vector,shown in FIG. 10 as cone-like rotation 280 while precessing about itsperpendicular axis. Note that the angle Θ between the plane of freelayer 336 and the magnetic direction 270 of PSC magnetic layer 350 willvary in this situation.

As seen in FIG. 5 and discussed above, PSC magnetic layer 350 has amagnetic direction that is in the plane of the layer. Because materialshaving face centered cubic (fcc) crystalline structures tend to havehigh in-plane anisotropy, they are used in the embodiments describedherein for in-plane PSC magnetic layer 350. In an embodiment, PSCmagnetic layer 350 is constructed of a NiFe alloy having an fcc crystalstructure. Ni—Fe compositions like permalloy (which comprisesapproximately 80% nickel and 20% Fe iron) have high magneticpermeability, soft magnetic properties (e.g., low easy axis coercivityand virtually no hard axis coercivity) and provide good spinpolarization of electrons passing there through. Note also thatpermalloy does not possess perpendicular magneto crystalline anisotropy(“PMA”). PMA is undesirable for in-plane magnetic layers, and is anotherreason to use permalloy.

Using a Ni—Fe permalloy results in an in-plane PSC layer 350 withmagnetic moments that are lower than the magnetic moment of free layer336, and can facilitate desired magnetization of PSC layer 350.

Seed layer 320 in the MTJ structure shown in FIG. 5 preferably comprisesTa, TaN, Cr, Cu, CuN, Ni, Fe or alloys thereof. First SAF layer 322preferably comprises either a Co/Ni or Co/Pt multilayer structure.Second SAF layer 326 preferably comprises either a Co/Ni or Co/Ptmultilayer structure plus a thin non-magnetic layer comprised oftantalum having a thickness of two to five Angstroms and a thin CoFeBlayer (0.5 to three nanometers). Anti-ferromagnetic coupling layer 324is preferably made from Ru having thickness in the range of three to tenAngstroms. Ferromagnetic coupling layer 328 can be made of Ta, W, Mo orHf having a thickness in the range of one to eight Angstroms. Tunnelingbarrier layer 334 is preferably made of an insulating material such asMgO, with a thickness of approximately ten Angstroms. Free layer 336 ispreferably made with CoFeB deposited on top of tunneling barrier layer334. Free layer 336 can also have layers of Fe, Co, Ni or alloysthereof. Spacer layer 340 over MTJ 330 can be any non-magnetic materialsuch as 2 to 20 Angstroms of ruthenium, 2-20 Angstroms of Ta, 2-20Angstroms of TaN, 2-20 Angstroms of Cu, 2-20 Angstroms of CuN, or 2-20Angstroms of MgO.

The manner in which a bit is written using the precessional spin currentMTJ structure 300 will now be described. In particular, an electricalcurrent is supplied, for example, by a current source 375, which passeselectrical current through the precessional spin current magnetic layer350, the non-magnetic spacer 340, the free magnetic layer 336, thenon-magnetic tunneling barrier layer 334, and the reference layer 332.The electrons of the electrical current passing through the precessionalspin current magnetic layer 350 become spin polarized in the magneticdirection thereof, thus creating a spin polarized current that passesthrough non-magnetic spacer layer 340, free magnetic layer 336,tunneling barrier layer 334, and reference magnetic layer 332. The spinpolarized current exerts a spin transfer torque on free magnetic layer336, which helps overcome the inherent damping of the magnetic materialmaking up the free layer 336. This assists the free magnetic layer 336to precess about its axis, which is shown in FIG. 4.

Once the magnetic direction of the free magnetic layer 336 begins toprecess, the magnetic direction of the PSC magnetic layer 350 begins torotate, as is also seen in FIG. 4. This rotation is caused by themagnetic and/or electronic coupling between the free magnetic layer 336and the PSC magnetic layer 350 through the non-magnetic spacer 340. Therotation of the magnetic direction of the PSC magnetic layer 350 causesthe spin polarization of the electrons of the electrical current tochange in a manner corresponding to the magnetic direction of the PSCmagnetic layer 350. Because the spin of the electrons of the spinpolarized current corresponds to the magnetic direction of PSC magneticlayer 350, and the magnetic direction of PSC magnetic layer 350 followsthe precession of free magnetic layer 336, the spin of the electronsapplies spin transfer torque to the free layer 336 in a direction thatvaries through an entire switching cycle. Thus, devices using PSCmagnetic layer 350 can provide spin transfer torque 205 for an entireswitching cycle.

In particular, the structure described herein utilizing PSC magneticlayer 350 and spacer layer 340 creates precessional magnetization thatprovides spin current to the free layer 336 of an MTJ throughout thewhole precession cycle and therefore significantly enhance the freelayer switching process, which will result in faster write times.

A flowchart showing a method 400 of manufacturing an embodiment of anMRAM stack 500 is illustrated in FIGS. 6A-BB. MRAM stack 500 isillustrated in FIG. 7. MRAM stack will be formed on a substrate, whichin an embodiment can be a silicon substrate and in other embodiments canbe any other appropriate substrate material. In step 402 seed layer 520is deposited. In an embodiment, seed layer 520 can be constructed bydepositing, at step 404, a TaN layer 504 and then, at step 406,depositing a Cu layer 506. In an embodiment, TaN layer 504 is a thinfilm having a thickness of five nanometers and Cu layer 506 is a thinfilm having a thickness of five nanometers. In alternative embodiments,TaN layer 504 can have a thickness ranging from 2 to 20 nanometers whileCu layer 506 can have a thickness ranging from 0 to 20 nanometers.

At step 408, first perpendicular synthetic antiferromagnetic layer 522is deposited. In an embodiment, first perpendicular syntheticantiferromagnetic layer 522 can comprise a Pt layer 508 (deposited atstep 410), a Co/Pt multilayer 510 (deposited at step 412) and a Co layer512 (deposited at step 414). In an embodiment, Pt layer 508 is a Pt thinfilm having a thickness of 0.7 nanometers. In other embodiments, Ptlayer 508 can comprise a Pt thin film having a thickness ranging from0.5 to 20 nanometers. Co/Pt multilayer 510 can comprise a thin film ofCo having a thickness of 0.6 nanometers and a thin film of Pt having athickness of 0.4 nanometers. In other embodiments, the Co layer of Co/Ptmultilayer 510 can have a thickness of 0.1 to 1 nanometers and the Ptlayer of Co/Pt multilayer 510 can have a thickness ranging from 0.1 to 1nanometers. In an embodiment, Co/Pt multilayer 510 is repeated such thatCo/Pt multilayer 510 comprises six Co/Pt multilayers. In an embodiment,Co layer 512 is a thin film having a thickness of 0.6 nanometers. Inother embodiments, Co layer 512 can have a thickness ranging from 0.1 to1.0 nanometers.

As seen in FIG. 7, first perpendicular synthetic antiferromagnetic layer522 has a magnetic vector having a direction perpendicular to its plane.The magnetic direction of first perpendicular syntheticantiferromagnetic layer 522 is fixed and will not change directions(i.e., rotate or precesses) under normal operating conditions. Thethickness of the layers are selected to have high anisotropy whilemanaging stray fields on free layer 536.

At step 416, exchange coupling layer 524 is deposited. In an embodiment,exchange coupling layer 524 comprises an Ru thin film having a thicknessof 0.8 nanometers, and in other embodiments can range from 0.3 to 1.5nanometers.

At step 418, second perpendicular synthetic antiferromagnetic layer 526is fabricated. Fabrication of second perpendicular syntheticantiferromagnetic layer 526 (step 418) comprises many steps, andincludes fabrication of reference layer 532 of magnetic tunnel junction530, as will be discussed. At step 420, Co layer 514 is deposited. In anembodiment, Co layer 514 is a thin film having a thickness of 0.3nanometers and in other embodiments, can have a thickness of 0.1 to 1.0nanometers. Thereafter, at step 420, a Co/Pt multilayer 516 isdeposited. In an embodiment, Co/Pt multilayer 516 comprises a thin filmof Co having a thickness of 0.6 nanometers and a thin film of Pt havinga thickness of 0.4 nanometers. In other embodiments, the thin film of Cocan have a thickness of 0.1 to 1.0 nanometers while the thin film of Ptcan have a thickness of 0.1 to 1.0 nanometers. Moreover, Co/Ptmultilayer 516 can comprise multiple Co/Pt layers as described herein.In an embodiment, Co/Pt multilayer 516 has two Co/Pt multilayers withthe thickness properties described above. After depositing Co/Ptmultilayer 516 at step 422, the method described herein deposits acobalt layer 518 at step 424. In an embodiment, Co layer 518 is a thinfilm having a thickness of 0.6 nanometers, while other embodiments, Colayer 518 can have a thickness in the range of 0.1 to 1.0 nanometers.Together, Co layer 514, Co/Pt layer 516 and Co layer 518 form a magneticstructure. The magnetic direction of the combination of Co layer 514,Co/Pt layer 516 and Co layer 518 is fixed, perpendicular to the plane ofeach layer, and antiparallel to the magnetic direction of firstperpendicular synthetic antiferromagnetic layer 522. The magneticproperties of the combination of Co layer 514, Co/Pt layer 516 and Colayer 518 will interact with the magnetic properties of reference layer532 of second perpendicular synthetic antiferromagnetic layer 526 togenerate a magnetic vector having a fixed magnetic direction that isalso perpendicular to the plane of each layer of second perpendicularsynthetic antiferromagnetic layer 526 (although variations of a severaldegrees are within the scope of what is considered perpendicular) andantiparallel to the magnetic direction of first perpendicular syntheticantiferromagnetic layer 522. These magnetic vectors are illustrated andFIG. 7, where it can be seen that the perpendicular syntheticantiferromagnetic layer 526 has a fixed and perpendicular magneticdirection that is antiparallel to the magnetic direction of firstperpendicular synthetic antiferromagnetic layer 522.

After deposition of Co layer 518 (step 424), a ferromagnetic couplinglayer 528 is deposited (step 526). In an embodiment, ferromagneticcoupling layer 528 is a thin film of Ta having a thickness of 0.2nanometers. In other embodiments, ferromagnetic coupling layer 528 canbe a thin film of Ta, W, Hf or Mo (or other appropriate material) havinga thickness ranging from 0.1 to 1.0 nanometers.

After deposition of ferromagnetic coupling layer 528 at step 426,reference layer 532 is deposited (step 428). Step 428, fabrication ofreference layer 532, comprises several steps, including deposition ofmagnetic layer 527 (step 430), deposition of a tungsten (W) layer 529(step 432) and deposition of magnetic layer 531 (step 434). In anembodiment, magnetic layer 527 comprises a thin film of CoFeB having athickness of 0.6 nanometers, where the alloy is sixty (60) percent Fe,twenty (20) percent Co and twenty (20) percent B. W layer 529 comprisesa thin film of W having a thickness of 0.2 nanometers. Magnetic layer531 comprises a thin film of CoFeB having a thickness of 0.8 nanometers,where the alloy is sixty (60) percent Fe, twenty (20) percent Co andtwenty (20) percent B. In other embodiments, magnetic layer 527 cancomprise a thin film of CoFeB having a thickness ranging from 0.5 to 1.0nanometers, W layer 529 can comprise a thin film having a thickness of0.1 to 1.0 nanometers, and magnetic layer 531 can comprise a thin filmof CoFeB having a thickness of 0.5 to 2.0 nanometers.

Reference layer 532 is constructed using magnetic materials so that ithas a magnetic vector having a magnetic direction perpendicular to itsplane, is fixed in direction, and is antiparallel to the magneticdirection of first perpendicular synthetic antiferromagnetic layer 522.As discussed and as seen in FIG. 7, the collective materials of thesecond perpendicular synthetic antiferromagnetic layer 526 have amagnetic vector having a magnetic direction that is perpendicular to theplane of each of its collective layers, is fixed in direction andantiparallel to the magnetic direction of first perpendicular syntheticantiferromagnetic layer 522. Note that the particular magnetic directionof first perpendicular synthetic antiferromagnetic layer 522 and secondperpendicular synthetic antiferromagnetic layer 526 is not important, solong as they are perpendicular to their respective planes andantiparallel to each other.

As discussed, reference layer 532 is one of the structures formingmagnetic tunnel junction 530. The flowchart showing the method ofmanufacturing MRAM stack 500, including magnetic tunnel junction 530,continues on FIG. 6B. At step 436, non-magnetic tunneling barrier layer534 is deposited on reference layer 532. In an embodiment, non-magnetictunneling barrier 534 is formed as a thin film of an insulatingmaterial, e.g., MgO. The purpose of non-magnetic tunneling barrier 534is discussed above. Manufacture of magnetic tunnel junction 530continues at step 438, when free layer 536 is deposited overnon-magnetic tunneling barrier 534. Fabrication of free layer 536comprises several steps. At step 440, a magnetic layer 535 is depositedover non-magnetic tunneling barrier 534. In an embodiment, magneticlayer 535 is comprised of a thin film of CoFeB having a thickness of 1.2nanometers, where the alloy is sixty (60) percent Fe, twenty (20)percent Co and twenty (20) percent B. In other embodiments, magneticlayer 535 can comprise a thin film of CoFeB or other suitable magneticmaterial having a thickness ranging from 0.5 to 2.0 nanometers.Manufacture of free layer 535 continues at step 442, where a W layer 537is deposited. In an embodiment, W layer 537 comprises a thin film of Whaving a thickness of 0.2 nanometers, and in other embodiments can athickness ranging from 0.1 to 1.0 nanometers. At step 444, manufactureof free layer 536 continues with forming magnetic layer 539. In anembodiment, magnetic layer 535 can comprise a thin film of CoFeB havinga thickness of 0.9 nanometers, where the alloy is sixty (60) percent Fe,twenty (20) percent Co and twenty (20) percent B. In other embodiments,magnetic layer 539 can comprise a thin film of CoFeB or other suitablemagnetic material having a thickness ranging from 0.5 to 1.5 nanometers.

Collectively, magnetic layers 535 and 539, along with non-magnetic Wlayer 537, form free magnetic layer 536. Free magnetic layer 536 has amagnetic vector having a magnetic direction perpendicular to its plane.In addition, free magnetic layer 536 design may include magnetization ofthe free layer 536 pointing a few degrees away from its perpendicularaxis. The tilted angle of the free layer magnetization can be due tointeraction with the PSC magnetic layer 550 or due to magnetocrystallineanisotropy, will additionally help switching of the free layermagnetization by improving the initiation of the switching. As seen inFIG. 7, the magnetic direction of free magnetic layer 536 can switch onehundred eighty (180) degrees from one direction to another,antiparallel, direction.

After fabrication of magnetic tunnel junction 530 at step 438, step 446is performed in which a spacer 540 is deposited. In an embodiment,spacer 540 can comprise a thin film of MgO having a thickness of 0.8nanometers. In other embodiments, spacer layer 540 can comprise a thinfilm of MgO having a thickness ranging from 0.5 to 1.5 nanometers. Inother embodiments, spacer layer 540 can be constructed as described inU.S. patent application Ser. No. 14/866,359, filed Sep. 25, 2015, andentitled “Spin Transfer Torque Structure For MRAM Devices Having A SpinCurrent Injection Capping Layer.” U.S. patent application Ser. No.14/866,359 is hereby incorporated by reference in its entirety.

After deposition of spacer layer 540, precessional spin current magneticlayer 550 is deposited (step 450). As seen in FIG. 6B, manufacture ofprecessional spin current magnetic layer 550 comprises several steps. Atstep 452, magnetic Fe layer 543 is fabricated over spacer layer 540. Inan embodiment, magnetic Fe layer 543 comprises a thin film of Fe havinga thickness of 0.6 nanometers. In other embodiments, magnetic Fe layer543 can comprise a thin film of Fe having a thickness ranging from 0.5to 2.0 nanometers.

At step 454, Ru layer 545 is deposited over magnetic Fe layer 543. In anembodiment, Ru layer 545 can comprise a thin film of Ru having athickness of 1.5 nanometers, and in other embodiments can comprise athin film of Ru having a thickness ranging from 0.4 to 5.0 nanometers.

At step 456, a magnetic NiFe layer 547 is deposited. In an embodiment,magnetic NiFe layer 547 comprises eighty (80) percent Ni and twenty (20)percent Fe, and has a thickness of 3.0 nanometers. In other embodiments,NiFe layer 547 can have a thickness ranging between 0.5 to 5.0nanometers. NiFe layer 547 can also comprise multiple layers. In onesuch embodiment, layer 547 comprises a thin film of CoFeB and NiFe. Inanother embodiment, layer 547 comprises NiFe layer in between layers ofCoFeB.

After manufacture of precessional spin current magnetic layer 550 atstep 450, a capping layer 551 is deposited (step 460). Manufacture ofcapping layer 551 can comprise depositing TaN layer 553 (step 462) anddepositing Ru layer (step 464). In an embodiment, TaN layer 553comprises a thin film of TaN having a thickness of 2.0 nanometers, whilein other embodiments, TaN layer 553 can have a thickness ranging from1.0 to 5.0 nanometers. In an embodiment, Ru layer 555 comprises a thinfilm of Ru having a thickness of ten (10) nanometers, while in otherembodiments, Ru layer 555 can have a thickness ranging from 1.0 to 20nanometers. In other embodiments, capping layer 551 comprise a layer ofRu (with no TaN) or a layer of MgO. The selection of a particularcapping structure is influenced, among several reasons, by theparticular annealing temperature to be used. This is due to the factthat these particular materials will have different characteristicsdepending on the annealing temperature.

Finally, at step 466, a hard mask 557 is deposited. Hard mask 557 cancomprise a layer of TaN having a thickness of 7.0 nanometers.

As shown in FIG. 7, precessional spin current magnetic layer 550 hasmagnetic direction that is in in-plane, and which can freely rotate inany magnetic direction. It is desirable for the magnetic vector ofprecessional spin current magnetic layer 550 to remain in-plane while itrotates. This is due to the fact, as seen in FIG. 4, that the more themagnetic vector of precessional spin current magnetic layer 550 remainsin plane during rotation, the more torque can be excerpted on themagnetic free layer 536, which aids in overcoming the damping 205 offree layer 536. Because it is desirable to keep the magnetic vector ofprecessional spin current magnetic layer 550 in-plane during rotation,the embodiments described herein utilize materials having high in-planeanisotropy.

Permalloy is a NiFe alloy having a face centered crystal structure.Permalloy comprised of approximately eighty (80) percent Ni and twenty(20) percent Fe and has soft magnetic properties (e.g., low easy axiscoercivity and almost no hard axis coercivity), and has good spinpolarization. Using permalloy for layer 547 of precessional spin currentmagnetic layer 550 (which resides at the PSC layer 550-TaN layer 551interface) thus provides an in-plane magnetic direction with magneticmoments that can be lower than the free layer magnetization.

Thus, in addition to NiFe layer 547, precessional spin current magneticlayer 550 can include an additional layer of Co, CoFeB or other Coalloys at the interface with TaN layer 551 and also at the interface ofNiFe layer 547 and Ru layer 545. One example of which could be a thinfilm of CoFeB (not shown in FIG. 7) in between NiFe layer 547 and TaNlayer 551 as well as between NiFe layer 547 and Ru layer 545. In such anembodiment, the CoFeB layer in between NiFe layer 547 and Ru layer 545can have a thickness ranging from one Angstrom to ten Angstroms. Use ofCoFeB layer can avoid the strong intermixing of NiFe layer 547 with TaNlayer 551. Note that in other embodiments, precessional spin currentmagnetic layer 550 may also have other layers to improve the interfaceproperties/performance in between NiFe layer 547, TaN layer 551 and Rulayer 545. Examples of such additional materials include Co or alloysincluding Co.

Other materials can be used at the interface of precessional spincurrent magnetic layer 550 and TaN layer 551, examples of which includeCo, Fe, and alloys containing these elements such as CoFeB. Likewise,choosing different Co—Fe ratios with various interfacial layers may makeit possible to obtain desired magnetizations for precessional spincurrent magnetic layer 550. Other embodiments of MRAM stack devices areshown in FIGS. 8 and 9. In these embodiments, the structures are similarto the embodiment described in the context of FIGS. 6A-6B and FIG. 7,the difference being the structure of the precessional spin currentmagnetic layer 550. In the MRAM device 600 shown in FIG. 8, precessionalspin current magnetic layer 550 comprises Fe layer 643 disposed overspacer 540. Fe layer 643 can comprise a thin film of Fe having athickness of 0.5 to 1.0 nanometers. In this embodiment, precessionalspin current magnetic layer 550 further comprises CoFeB layer 647. CoFeBlayer 647 can have a thickness ranging from 0.5 to 4.0 nanometers.

Another embodiment of MRAM stack 700 is shown in FIG. 9. In theembodiment shown in FIG. 9, precessional spin current magnetic layer 550comprises Fe layer 743 over spacer 540. Fe layer 743 comprises a thinfilm of Fe having a thickness ranging from 0.5 to 1.0 nanometers. NiFelayer 745 is disposed over Fe layer 743. NiFe layer 745, such aspermalloy, as discussed, is a material having a face centered cubiccrystal structure and can have a thickness ranging from 1.0 to 5.0nanometers. As in embodiments discussed herein, NiFe layer 745 can beeighty percent Ni and twenty percent Fe. In this embodiment,precessional spin current magnetic layer 550 also comprises CoFeB layer747. CoFeB layer 747 can have a thickness ranging from 0.5 to 1.5nanometers.

The materials are chosen so that the magnetization of precessional spincurrent magnetic layer 550 can be set independently while alsocontrolling the out of plane magnetization component of the PSC layerthat impacts the freelayer switching performance.

FIG. 11 is a graph of the thin film vibrating sample magnetometer (VSM)major hysteresis loop data for perpendicular magnetic tunnel junctiondevices having a precessional spin current magnetic layer 550. To obtainthis VSM) major hysteresis loop (labeled as 1105 in FIG. 11), a DC fieldwas applied. The applied field started at −14000 Oersteds, which thendecreased to 0.00 Oersteds, before rising to +14000 Oersteds. Theapplied field was then decreased steadily from +14000 Oersteds to 0.00Oersteds, before increasing to −14000 Oersteds. Positive and negativesigns of the DC applied field indicate in-plane applied field directionsof the field sweep. VSM measurements, shown as normalized magneticmoment on the Y axis of the graph in FIG. 11, were taken with the DCmagnetic field applied in the plane of the sample, i.e., along the hardaxis of the magnetic tunnel junction 530. The sharp transition aroundzero applied field (zero Oersteds), pointed to by arrows 1110A and1110B, indicates that precessional spin current magnetic layer 550 isin-plane magnetized, i.e., magnetized along the easy axis.

FIG. 12 shows the ferromagnetic resonance of a magnetic tunnel junctiondevice 500 having precessional spin current magnetic layer 550 measuredat twenty four (24) GHz. The magnetic field was applied in perpendiculardirection. Dashed line 1010 at 8000 Oersteds indicates the regionboundary ω/γ ˜8.0 kGauss at 24 GHz between in-plane precessional spincurrent magnetic layer 550 and perpendicular magnetized free magneticlayer 536. According to the resonance equation: ω/γ=H_(res)−4πM_(eff),resonance of precessional spin current magnetic layer 550 indicatesstrong in-plane magnetization. The effective magnetization values showeffective perpendicular anisotropy of the free layer (4πM_(eff)˜−4.0kGauss) and strong effective in-plane anisotropy of the PSC layer(4πM_(eff)˜7.5 kGauss).

An alternative embodiment is shown in FIG. 13. In this embodiment,magnetic device 1300 has had its MTJ stack inverted with respect to theembodiment shown in FIG. 5. In particular, magnetic device 1300 includesa seed layer 1370. Precessional spin current magnetic layer 1350 isplaced over seed layer 1370. Precessional spin current magnetic layer1350 can comprise any of the embodiments described in the context ofFIGS. 5 and 7-9, with the layers inverted. As an example, precessionalspin current magnetic layer 1350 can comprise a magnetic NiFe permalloylayer 547 over seed layer 1370, Ru layer 1345 over NiFe permalloy layer547, and magnetic Fe layer over Ru layer 1345. As discussed, NiFepermalloy layer 547 can be replaced with other face centered materialswithout departing from the scope of the teachings of the patentdocument.

Nonmagnetic spacer 1340 is placed over PSC layer 1350. Nonmagneticspacer 1340 has the same properties, construction and characteristics asnonmagnetic spacer 340 and 540, discussed above. MTJ 1330 is placed overnonmagnetic spacer 1340. MTJ 1330 is generally constructed of free layer1336 (which is placed over nonmagnetic spacer 1340) and reference layer1332. Free layer 1336 and reference layer 1332 are spatially separatedfrom each other by tunneling barrier layer 1334, which is made of aninsulating material such as MgO. As above, MTJ 1330 as a perpendicularMTJ in that the magnetic direction of both reference layer and freelayer are perpendicular to their respective planes. As discussed withrespect to other embodiments, free magnetic layer 1336 design mayinclude magnetization of the free layer 1336 pointing a few degrees awayfrom its perpendicular axis. The tilted angle of the free layermagnetization can be due to interaction with the PSC magnetic layer 1350or due to magnetocrystalline anisotropy, will additionally helpswitching of the free layer magnetization by improving the initiation ofthe switching. Ferromagnetic coupling layer 1328 is placed overreference layer 1332. A synthetic antiferromagnetic (SAF) layer 1326 isdisposed over ferromagnetic coupling layer 1328. An antiferromagneticcoupling layer 1324 is placed over SAF layer 1326. Another syntheticantiferromagnetic layer 1322 is placed over antiferromagnetic couplinglayer 1324. Note that SAF layer 1326 technically also includesferromagnetic coupling layer 1328 and reference layer 1332, but areshown separately here for explanation purposes. SAF layers 1326 and 1322also perpendicular magnetic directions. Finally, capping layer 1320 isplaced over SAF layer 1320. Current can be provided by a current source1374. Other than the ordering of the layers, magnetic device operates inthe same manner as described with respect to the embodiment shown inFIGS. 5 and 7. Thus, just as shown in FIGS. 5 and 7, PSC magnetic layer1350 rotates in such a way that spin transfer torque 310 is applied in abeneficial manner throughout the entire precession cycle of free layer1336.

All of the layers of devices 300, 500, 600, 700 and 1300 illustrated inFIGS. 5, 7-9 and 13 can be formed by a thin film sputter depositionsystem as would be appreciated by one skilled in the art. The thin filmsputter deposition system can include the necessary physical vapordeposition (PVD) chambers, each having one or more targets, an oxidationchamber and a sputter etching chamber. Typically, the sputter depositionprocess involves a sputter gas (e.g., argon, krypton, xenon or the like)with an ultra-high vacuum and the targets can be made of the metal ormetal alloys to be deposited on the substrate. Thus, when the presentspecification states that a layer is placed over another layer, suchlayer could have been deposited using such a system. Other methods canbe used as well. It should be appreciated that the remaining stepsnecessary to manufacture MTJ stack 300 are well-known to those skilledin the art and will not be described in detail herein so as not tounnecessarily obscure aspects of the disclosure herein.

It should be appreciated to one skilled in the art that a plurality ofMTJ structures 300 can be manufactured and provided as respective bitcells of an STT-MRAM device. In other words, each MTJ stack 300, 500,600, 700 and 1300 can be implemented as a bit cell for a memory arrayhaving a plurality of bit cells.

The above description and drawings are only to be consideredillustrative of specific embodiments, which achieve the features andadvantages described herein. Modifications and substitutions to specificprocess conditions can be made. Accordingly, the embodiments in thispatent document are not considered as being limited by the foregoingdescription and drawings.

What is claimed is:
 1. A method of manufacturing a magnetic device overa substrate, comprising: forming a synthetic antiferromagnetic structurein a first plane, the synthetic antiferromagnetic structure comprising amagnetic reference layer, the magnetic reference layer having amagnetization vector that is perpendicular to the first plane and havinga fixed magnetization direction; forming a non-magnetic tunnel barrierlayer in a second plane and over the magnetic reference layer; forming afree magnetic layer in a third plane and over the non-magnetic tunnelbarrier layer, the free magnetic layer having a magnetization vectorthat is perpendicular to the third plane and having a magnetizationdirection that can precess from a first magnetization direction to asecond magnetization direction, the magnetic reference layer, thenon-magnetic tunnel barrier layer and the free magnetic layer forming amagnetic tunnel junction; forming a non-magnetic spacer in a fourthplane and over the free magnetic layer, the non-magnetic spacercomprising MgO; forming a precessional spin current magnetic layer in afifth plane that is physically separated from the free magnetic layerand coupled to the free magnetic layer by the non-magnetic spacer, theprecessional spin current magnetic layer having a magnetization vectorwith a magnetization component that is located within the fifth planeand can freely rotate in any magnetic direction in the fifth plane, theprecessional spin current magnetic layer comprising an Fe layer, an Rulayer, and a face centered cubic (fcc) crystal structure layercomprising a material having a fcc crystal structure, the Fe layer beingdisposed over the non-magnetic spacer, the Ru layer being disposed overthe Fe layer, and the fcc crystal structure layer being disposed overthe Ru layer; and forming a capping layer in a sixth plane and over theprecessional spin current magnetic layer.
 2. The method of claim 1,wherein electrical current is directed through the capping layer, theprecessional spin current magnetic layer, the non-magnetic spacer, thefree magnetic layer, the non-magnetic tunnel barrier layer, and themagnetic reference layer, wherein electrons of the electrical currentare aligned in a magnetic direction of the precessional spin currentmagnetic layer; and a magnetization direction of the precessional spincurrent magnetic layer is free to follow precession of a magnetizationdirection of the free magnetic layer, thereby causing spin transfertorque to assist switching of the magnetization vector of the freemagnetic layer.
 3. The method of claim 1, wherein a magnetizationdirection of the magnetization vector of the precessional spin currentmagnetic layer is in the fifth plane.
 4. The method of claim 1, whereina magnetization direction of the precessional spin current magneticlayer has a magnetization component in the fifth plane which can freelyrotate in the fifth plane.
 5. The method of claim 1, wherein thematerial having the fcc crystal structure is permalloy comprising nickel(Ni) and iron (Fe).
 6. The method of claim 1, wherein the capping layercomprises a layer of TaN.
 7. The method of claim 1, wherein theprecessional spin current magnetic layer further comprises a CoFeB layerdisposed over the Fe layer and under the fcc crystal structure layer. 8.The method of claim 7, wherein the material having the fcc crystalstructure is permalloy comprising nickel (Ni) and iron (Fe).
 9. Themethod of claim 8, wherein the capping layer comprises a layer of TaN.10. The method of claim 1, wherein the precessional spin currentmagnetic layer further comprises a first CoFeB layer and the fcc crystalstructure layer comprising the material having the fcc crystal structureand a second CoFeB layer, the Fe layer being disposed over thenon-magnetic spacer, the Ru layer being disposed over the Fe layer, thefirst CoFeB layer being disposed over the Fe layer, the fcc crystalstructure layer being disposed over the first CoFeB layer, and thesecond CoFeB layer being disposed over the fcc crystal structure layer.11. The method of claim 10, wherein the material having the fcc crystalstructure is permalloy comprising nickel (Ni) and iron (Fe).
 12. Themethod of claim 11, wherein the capping layer comprises a layer of TaN.13. The method of claim 11, wherein the capping layer comprises a layerof MgO.
 14. The method of claim 11, wherein the capping layer comprisesa layer Ru.
 15. The method of claim 1, wherein the material having thefcc crystal structure is a NiFe layer, and the precessional spin currentmagnetic layer further comprises a layer being disposed over the NiFelayer.
 16. The method of claim 15, wherein the layer disposed over theNiFe layer comprises CoFeB.
 17. The method of claim 1, wherein theprecessional spin current magnetic layer is magnetically coupled to thefree magnetic layer.
 18. The method of claim 1, wherein the precessionalspin current magnetic layer is electronically coupled to the freemagnetic layer.
 19. The method of claim 1, wherein precession of theprecessional spin current magnetic layer is synchronized to precessionof the free magnetic layer.
 20. The method of claim 1, wherein theprecessional spin current magnetic layer has a rotation frequencygreater than zero.
 21. The method of claim 1, wherein the free magneticlayer has an effective magnetic anisotropy such that its easymagnetization axis points away from a perpendicular direction and formsan angle with respect to its perpendicular plane.